Reagent conditioning for electrostatic separation of minerals



Patented Apr. 22, 1952 REAGENT CONDITIONING FOR. ELECTED- STATICSEPARATION OF MINERALS Foster Fraas, Riverdale, Md;, assignor' to the"United States of America as represented by the Secretary of theDepartment or the Interior No Drawing. Application January 16, 1942i,Serial No. 2,800

(Granted under the act of March 3, 1883', as amended April30, 1928; 370O; G. 757) 2 Claims.

The invention described herein maybe manufactured-and used by or for theGovernment of the United States for governmental purposes withoutthepayment to me of any royalty thereon in accordance with the provisionsof the act of April 30, 1928 (Ch. 460, 45 Stat. L. 467-).

This invention relates to the electrostatic separation of minerals. Itparticularly relates to the conditioning of mineral surfaces torenderthe" various minerals more amenable to electrostatic separation. Stillmore particularly the invention relates to' conditioning mineralcomposites with anionic reagents and then subjecti'ng'the treatedcomposite to electrostatic separation.

Refractory type minerals (i. e., those not easily susceptible tochemical attack) when in combination, such as kyanite zircon', yield butslightly to electrostatic separation. Such separations are improved ifthe crushed mineral composite is deslimed or cleaned by dedusting or bymoderate agitation with water. Theintroduction of acids such ashydrofluoric and sulfuric acids to the water during the deslimingimproves electrostatic separation somewhat; however, the degree ofimprovement frequently is not suflicient to War-' rant independentcommercial application of the acids alone.

Accordingly, it is an object of this invention to provide a methodwhereby the surfaces of reiractory mineral-composites are conditionedwith anionic reagents and the composite thereby rendered more amenableto electrostatic separation. Other objects and advantageswill. beapparent and in part hereinafter appear. 7

These objects and advantages are accomplished in accordance-with theinvention by heating and drying, a ground and deslimed mineralcomposite, thereafter treating said hot dry composite with a selectivesurface conditioning reagent, and then subjecting the conditionedcomposite to electrostatic separation whereby the selectively con-'-ditioned constituent is rendered more or less susceptible to theinfluence of an electrical poten-- tial differential than theunconditioned constituent; and thereby rendering. said composite more 2been found to be greatly improved by surface conditioning treatment inaccordance with this invention.

In the present process the heating and drying of the mineral compositecan be suitably accomplished by any heating and drying meansg'e'ns.erallyadapted to such operations.

Suitable surface conditioning reagents for urposes of this inventioninclude organic compounds which exhibit anionic and cationiccharacteristics. The presently preferred anionic conditloning agents arethose having the following general structural formula:

R(-CO0H)n wherein R is a normal, branched or cyclic h'y' drocarbonappendage, and n' is any wholenum ber consistent'with the nature of R.Such sub-' stances include normal aliphatic acids such as heptylic acid,propionic acid, acetic acid; mixed coconut fatty acids, crotonic acid,oleic acid'arid' the like; dibasic acids such as fumaric acid 'an'd' thelike; aryl acids such as? benzoic' acid, the naphthenic acids,salicyclic acid, phthalic acid, cresylic acid, and the like; and otherorganic compounds having acid properties and a hydrocarbon appendage ofsufficient'length. Although cresylic acid has a hydroxyl group insteadofa carboxyl, the hydro'xyl group attached to an aryl appendage exhibitsacid properties.

In operation the mineral composite is first crushed to a degreewhichwill substantially liberate the various mineral constituents fromone another. This can be accomplished by any siiitable materialsdisintegrating means. The ground material is thereafter mixed with wateror other suitable suspending medium to form a pulp containing? about 50to "per cent solids and then deslimed. The desliming' can beaccomplished by treating the pulp with about 0105 to 50' pounds of atleast'one mineral acid per ton of composite in the pulp. Mineral acidssuchas hydrochloric, hydrofluoric, nitric, phosphoric, sulfuric,sulfurous and the like have been found to be satisfactory: for thispurpose. Mixtures of hydrofluoric acidor' fluoride salts with otheracids, such. as sulfuricghavealso been found to be-efiective in thisconnection. When such mixtures are em ployed a-"few' tenths of a poundof the'hydrofluoric aoid'or fluoride and lto 50 pounds of sulfuric acidis" generally sufficient.

The time for this initial desiinfingand; surface cleaning treatment isnot critical and will vary greatly with the nature of the mineral, thedegree of fineness of the crushed composite, the rate of agitation andother such factors. About one-half an hour has generally been found tobe sufiicient for agitation. The liquid phase is thereafter removed fromthe treated solids by suitable solid-liquid separating means such assedimentation and decantation, filtration, centrifuging, and the like.Thereafter the deslimed composite is preferably washed with sufiicientwater to remove any liquids which may be entrapped. in the mass. Thedewatered composite is then dried. Any suitable method can be employedto dry the mineral composite. Merely *heating or passing hot dry airthrough the mass has been found to dry the material satisfactorily.

Thereafter to each ton of the hot dry material about 0.05 to pounds ofan anionic reagent is added and intimately mixed therewith. Thetemperature of this conditioning treatment will vary somewhat with thereagent employed and the mineral being treated. In general temperaturesbetween about 50 to 300 degrees centigrade, or temperatures sufilcientto volatilize the reagent have been found satisfactory. The reagent canbe added as a solid, liquid or gas. Some anionic reagents such asbenzoic acid are sufilciently volatile so that they can be added in purestate without any danger of adding an excessive amount or of failing toget a uniform distribution of the reagent throughout the composite.Other less volatile reagents, such as the coconut fatty acids, can beadded as solutions in suitable volatile solvents such as carbontetrachloride, gasoline, kerosene, and the like, in order to achieve agreater control of the amount of reagent added and a greater uniformityof dispersion. The conditioning treatment can be accomplished by any ofthe many well known processes for intimately and uniformly blendingsmall amounts of materials with larger amounts of crushed solidmaterials. For example, the hot dry material can be tumbled with thereagent for a sumcient time to insure a substantially uniform dispersionor contacting of the reagent and the material being treated. Thereafterthe thus treated composite is immediately passed through anelectrostatic separation.

The following examples will show more specifically how the invention maybe carried out but it is not limited thereto.

' EXAMPLE I A ground kyanite-zircon composite was moderately agitatedwith four pounds of hydrofluoric acid'per ton, in a 60 to '70 per centsolids pulp. The desliming liquid was removed by sedimentation'anddecantation. This was followed by washing the deslimed material severaltimes with water and then dewatering by sedimentation and decantation.The material was dried by heating and agitating the mass; the hot drymaterial was then at the stage for the anionic reagent treatment. Toseparate batches of the hot dry deslimed composite anionic reagents wereadded and intimate- 1y.blended by rolling and stirring the mixture. Thereagents were added in a concentration equivalent to three pounds ofreagent per ton of composite. The thus treated material was immediatelypassed through a single stage roll-type separator having a non-ionizingnegative electrode adjacent to the roll. A partial summary of theresults is given in Table I below. The defiectant is the fractionattracted toward the electrode, while the residue remains close to theroll.

TABLE I Efiect of various reagents on the kyamte-ztrcon separattcmZircon, per cent Test Weight No Treatment Product Percent Fraction Assayof Total defiectant. 27 56 32 1.-.. None residue... 73 43 68 composite.47 100 deflectant- 28 66 63 2--.. Benzoicacid residue... 72 15 37composite. 100 29 100 deflectant. 23 75 74 3..-. Salicylicacidresidue... 77 8 26 composite. 100 20 100 4.--. Phthalic deflectant. 2648 65 Anhydride residue-... 74 9 35 composite. 100 19 100 defleetant. 1475 24 6---. Oxalicacid residue... 86 40 76 composite. 100 45 100defiectant. 34 77 93 6.... Hoptylicacid.- residue... 66 3 7 composite.100 28 100 dcfiectant. 30 74 (i9 7---. Cresylic acid {residue.-.. 70 1431 composite. 100 32 100 From these results it can be seen that animprovement can be obtained by treatment with anionic reagents ingeneral. The data also shows that oxalic acid, unlike the other reagentsin having no hydrocarbon appendage, does not ive any appreciableimprovement in separation.

This process of conditioning with anionic reagents was extended to othercombinations of minerals. The same conditioning process was used but theelectrostatic separation was more elaborate, the separator had sixstages instead of one as in Example I. The first three stages hadnegative electrodes with the non-deflectant passed through successivestages to yield a tailing. The defiectant from each of the three stageswas combined as heads for the second three stages. The second threestages had positive electrodes with the non-defiectant passed throughsuccessive stages to yield the concentrate. The deflectant from each ofthe three stages yields a middling fraction which may in some casescontain a third mineral component which is electrically conduc tive.

EXAMPLE II A sillimanite-quartz composite was deslimed as in Example I.Some portions of the deslimedcomposite were not treated with any anionicreagent; and used as controls. Other portions were anionicallyconditioned as in Example I. The materials were then subjected toelectrostatic separation. The collected portions were assayed by a sinkand float procedure in acetyline tetra- This shows an improvement inboth grade and recovery by the use of benzoic acid as the conditioningreagent. Other anionic reagents had a similar effect.

5 EXAMPLE III TABLE III E 7 2015 beneoic acid on a icyomite-quartzseparation Tailing Size Analysis Per cent Kyanite Tail- Weight Per centing Composition Treatment 10+14 14+20 10|14 l4+20 mesh mesh mesh mcshNoncnh; 27 9.3 4.1 13.2 Benzoic acid 3. 7 0, 5 3. 7 10. 2

In addition to improving the recovery of the kyanite, the benzoic acidenables the processing of coarser-sized material. It also counteractssensitivity to high humidityweather conditions.

From the above description and examples, it is apparent that a definiteimprovement in the electrostatic separation of refractory mineralcomposites is obtained by the conditioning of the mineral surfaces withanionic reagents.

While the invention is particularly described in connection with aconditioning treatment with anionic reagents such as benzoic acid,phthalic acid, heptylic acid and the like, it is not limited thereto,certain basic reagents such as the amines also function in a similarmanner.

Since many widely diifering embodiments of the invention will occur toone skilled in the art, the invention is not limited to the specificdetails illustrated and described, and various changes may bemadetherein without departing from the spirit and scope thereof.

What is claimed is:

1. In a process'for the electrostatic separation of the liberated anddeslimed constituents of a mineral composite of a type resistant tochemical attack and of the class consisting of lryanitezircon,sillimanite-quartz, and kyanite-quartz, which involves electrostaticseparation of the composite constituents, the steps prior to saidseparation which comprise heating and drying said composite and thentreating said hot dry composite with about 0.05 to 5 pounds of anorganic anionic conditioning agent per ton of composite, saidconditioning agent being a carboxylic acid having a hydrocarbonappendage, whereby at least one of said composite constituents isselectively filmed with said conditioning agent and said compositeconstituents are thereby rendered more amenable to electrostaticseparation.

2. The process of claim 1 wherein the anionic conditioning agent is ofthe group of compounds having the formula R(COOH)n wherein: R is anormal, branched, or cyclic hydrocarbon appendage and n is any wholenumber consistent with the chemical nature of R. FOSTER FRAAS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS OTHER REFERENCES Fraas and Ralston, ElectrostaticSeparations of Solid, Industrial and Engineering Chemistry, vol. 32, No.5, pages 600 to 644.

1. IN A PROCESS FOR THE ELECTROSTATIC SEPARATION OF THE LIBERATED ANDDESLIMED CONSTITUENTS OF A MINERAL COMPOSITE OF A TYPE RESISTANT TOCHEMICAL ATTACK AND OF THE CLASS CONSISTING OF KYANITEZIRCON,SILLIMANITE-QUARTZ, AND KYANITE-QUARTZ, WHICH INVOLVES ELECTROSTATICSEPARATION OF THE COMPOSITE CONSTITUENTS, THE STEPS PRIOR TO SAIDSEPARATION WHICH COMPRISE HEATING AND DRYING SAID COMPOSITE AND THENTREATING SAID HOT DRY COMPOSITE WITH ABOUT 0.05 TO 5 POUNDS OF ANORGANIC ANIONIC CONDITIONING AGENT PER TON OF COMPOSITE, SAIDCONDITIONING AGENT BEING A CARBOXYLIC ACID HAVING A HYDROCARBONAPPENDAGE, WHEREBY AT LEAST ONE OF SAID COMPOSITE CONSITITUENTS ISSELECTIVELY FILMED WITH SAID CONDITIONING AGENT AND SAID COMPOSITECONSTITUTENTS ARE THEREBY RENDERED MORE AMENABLE TO ELECTROSTATICSEPARATION.